Grargar: snip

Grargar: I don't think it's supported by GOG itself. When I do it, I do it through an external site like . <a href="http://www.gog.com/forum/general_archive/how_to_format_text_as_strikethrough/post3" class="link_arrow"></a></div> Indeed, that's exactly the site I've used as well. [url=http://www.gog.com/forum/general/the_favourite_foursomes_ga/post64]Quite recently, in fact: Although, the fact that the text CAN be rendered via copy/paste would seem to...suggest, at least, that it should be possible. It certainly would be more convenient.

No, it is not.
What you are doing in your example is using this technique: http://en.wikipedia.org/wiki/Strikethrough#Unicode
So, in fact, you are not writing "the mighty game Gauntlet" and then striking it. It just looks like it for your eye, but for the browser your are writing something different (different characters).

The way I do it, is quote a post with strike-through text and copy paste the letters I needed...
a̶ b c d e̶ f g̶ h̶ i̶ j k l̶ m̶ n̶ o p q r s t̶ u̶ v w x y̶ z from the post above , or
a̶ ̶b̶ ̶c̶ ̶d̶ ̶e̶ ̶f̶ ̶g̶ ̶h̶ ̶i̶ ̶j̶ ̶k̶ ̶l̶ ̶m̶ ̶n̶ ̶o̶ ̶p̶ ̶q̶ ̶r̶ ̶s̶ ̶t̶ ̶u̶ ̶v̶ ̶w̶ ̶x̶ ̶y̶ ̶z̶ A̶ ̶B̶ ̶C̶ ̶D̶ ̶E̶ ̶F̶ ̶G̶̶̶ ̶H̶ ̶I̶ ̶J̶ ̶K̶ ̶L̶ ̶M̶ ̶N̶ ̶O̶ ̶P̶ ̶Q̶ ̶R̶ ̶S̶ ̶T̶ ̶U̶ ̶V̶ ̶W̶ ̶X̶ ̶Y̶ ̶Z̶ I generated from the linked site.
Obviously it's an overkill, but I don;t use it that much anyway